Wrap-up quiz M3 needs some maintainance

[ArturoAmorQ]

There are a couple of things that I've noticed that should be updated:

• As reported in this forum comment, we don't clarify in the instructions that at a first stage we expect students to use the whole dataset when comparing models (we later use nested cross-validation, also on the whole dataset);
• We provide the students with a list of preprocessors to evaluate:

all_preprocessors = [
    None,
    StandardScaler(),
    MinMaxScaler(),
    QuantileTransformer(n_quantiles=100),
    PowerTransformer(method="box-cox"),
]

Even if it works for this small dataset, using "passthrough" is better than using None (I don't know if this behavior is documented somewhere in the scikit-learn doc).

[ArturoAmorQ]

Partially addressed in MR 91 in our private repo.